Single-cavity toroidal continuously variable transmissions used as a transmission mainly for automobiles include a toroidal transmission mechanism (variator) where an input-side disc and an output-side disc, each of surfaces of which opposite to each other have a concave cross section of a circular arc shape, and freely rotatable power rollers clamped between these discs are combined. The input-side disc is coupled to drive an input shaft such that the input-side disc can move along the input shaft to which torque is input while the output-side disc is attached opposite to the input-side disc such that the output-side disc is rotatable relative to the input shaft and that movement away from the input-side disc is limited.
In such a single-cavity toroidal continuously variable transmission, when the input-side disc rotates, the output-side disc inversely rotates via the power rollers and thus rotary motion input to the input shaft is transferred to the output-side disc as inverse rotary motion, which is then transferred from an output gear rotating integrally with the output-side disc. Here, shifting an inclination angle of a rotation axis of the power roller such that a peripheral surface of the power roller abuts against near each of an outer periphery of the input-side disc and the center of the output-side disc increases the speed from the input shaft to the output gear. Inversely, shifting the inclination angle of the rotation axis the power roller such that the peripheral surface of the power roller abuts against near each of the center of the input-side disc and an outer periphery of the output-side disc decreases the speed from the input shaft to the output gear. Moreover, intermediate gear ratios can also be obtained substantially continuously by adjusting the inclination angle of the rotation axis of the power roller as appropriate.
Furthermore, such a single-cavity toroidal continuously variable transmission includes an output-side bearing that is provided behind the output gear and supports a thrust load applied from the output-side disc, an input-side bearing that is provided at an end portion of the input shaft on the side of the output-side disc and supports a thrust load applied from the input-side disc, and a pressing mechanism that presses at least one of the input-side disc and the output-side disc toward a direction such that the input-side disc and output-side disc approach each other.
As one example of such a single-cavity toroidal continuously variable transmission, the one disclosed in Patent Literature 1 is known.
In this single-cavity toroidal continuously variable transmission, an input-side bearing supporting an input shaft having relatively small torque is smaller than an output-side bearing supporting an output shaft having relatively large torque and an input-side inner race and output side inner race of the input-side bearing and output-side bearing are separately provided while an outer race thereof is formed integrally. This allows for downsizing a size of the input-side bearing in the shift direction as well as reducing rolling resistance of the input-side bearing.
Moreover, as another example of the single-cavity toroidal continuously variable transmission as described above, the one disclosed in Patent Literature 2 or the one illustrated in FIG. 3 is known.
The one illustrated in FIG. 3 and the one disclosed in Patent Literature 2 have substantially the same configuration except for the pressing mechanism. Therefore, the one illustrated in FIG. 3 is described here while descriptions on the one disclosed in Patent Literature 2 is omitted.
FIG. 3 is a cross-sectional view illustrating a single-cavity toroidal continuously variable transmission. In FIG. 3, symbol 1 denotes an input shaft, 2 denotes an input-side disc, 3 denotes an output-side disc, 4 denotes a power roller, and 5 denotes a pressing mechanism that presses the input-side disc 2 toward the output-side disc 3.
Incidentally, the power roller 4 is supported in a freely rotatable manner by a trunnion not illustrated.
The pressing mechanism 5 is hydraulic and provided in a manner rotatable integrally with the input shaft 1 and includes a cylinder 51 that forms a hydraulic chamber between a back surface of the input-side disc 2 and the cylinder 51 and a first and second pistons 55 and 56 that is provided inside the cylinder 51 and reciprocates in a direction along the input shaft 1 by hydraulic pressure.
A tip end portion of the cylinder 51 is engaged with an outer peripheral portion of the input-side disc 2 in an integrally rotatable manner and the input-side disc 2 is fit to the input shaft 1 in a movable manner along the shaft direction. Therefore, when the input shaft 1 rotates, the cylinder 51 also rotates with the input shaft 1. Due to rotation of the cylinder 51, the input-side disc 2 engaged to the cylinder 51 also rotates.
Furthermore, the input-side disc 2 is pressed toward the output-side disc 3 when oil is supplied to a first oil chamber 50a and a second oil chamber 50b. That is, when oil is supplied to the first oil chamber 50a, the input-side disc 2 is pressed toward the output-side disc 3 by hydraulic pressure since leftward movement of the first piston 55 is limited. Also, when oil is supplied to the second oil chamber 50b, the input-side disc 2 is pressed toward the output-side disc 3 by the second piston 56. Moreover, when oil is supplied to the second oil chamber 50b, the input shaft 1 is pulled leftward via the cylinder 51. This results in a thrust load applied to an input-side bearing 10, which will be described later. Incidentally, the first oil chamber 50a is provided with a disc spring 57 that applies a preload. This disc spring 57 also presses the input-side disc 2 toward the output-side disc 3.
The output-side disc 3 is supported by the input shaft 1 via a needle bearing in a freely rotatable manner. Furthermore, the output-side disc 3 is spline-connected to an outer periphery of one end portion of an output shaft (flange) 7 of a cylindrical shape formed integrally with an output gear 6 for output. This allows for the output-side disc 3 and output gear 6 to rotate integrally. The other end portion of the output shaft 7 is supported by a casing (not illustrated) via an output-side bearing 11. Therefore, the output-side disc 3 is limited of rightward movement along the input shaft 1 by the output-side bearing 11 via the output gear 6. Therefore, when the pressing mechanism 5 presses the input-side disc 2 toward the output-side disc 3, the output-side disc 3 is pressed rightward via the power roller 4, which results in a thrust load applied to the output-side bearing 11 via the output shaft 7.
Moreover, a right end portion of the input shaft 1 is spline-connected to a shaft portion 8a of an input gear 8 for rotation with the input shaft 1 and is limited of movement toward the right end side of the input shaft 1 by a nut 9. Also, the shaft portion 8a of the input gear 8 is supported by a casing (not illustrated) via the input-side bearing 10.
Therefore, as described above, when the input shaft 1 is pulled leftward by the pressing mechanism 5, the input-side bearing 10 is applied with a thrust load via the input gear 8.
Incidentally, the input-side bearing 10 and output-side bearing 11 are angular bearings and arranged back to back.
In such a single-cavity toroidal continuously variable transmission, the input-side bearing 10 to support the thrust load applied from the input-side disc 2 and the output-side bearing 11 to support the thrust load applied from the output-side disc 3 are in the same size.
Moreover, still another example of the single-cavity toroidal continuously variable transmission as described above is illustrated in FIG. 4.
FIG. 4 is a cross-sectional view illustrating a single-cavity toroidal continuously variable transmission. In FIG. 4, symbol 1 denotes a shaft (supporting shaft), 2 denotes an input-side disc, 3 denotes an output-side disc, 4 denotes a power roller, and 5 denotes a pressing mechanism that presses the input-side disc 2 toward the output-side disc 3.
The pressing mechanism 5 is a loading cam type. That is, the shaft (supporting shaft) 1 is provided with the input-side disc 2 in a freely rotatable manner therearound and movable therealong. A cam plate 13 is arranged on a back surface side of the input-side disc 2. This cam plate 13 has a disc shape and includes a cylindrical portion in the center. A cylindrical shaft portion 14a of an input gear 14 is inserted in and fixed to this cylindrical portion. The shaft (supporting shaft) 1 is inserted through an inner diameter side of the shaft portion 14a. The shaft portion 14a is supported by the shaft (supporting shaft) 1 in a freely rotatable manner via a bearing. The cam plate 13 rotates integrally with the input gear 14.
A side surface of the input gear 14 facing the cam plate 13 side includes a concave portion. This concave portion is provided with a disc spring 15 that applies a preload. This disc spring 15 presses the cam plate 13 toward the input-side disc 2.
Furthermore, a plurality of rollers 16 are provided between the input-side disc 2 and cam plate 13. When the input gear 14 rotates, the cam plate 13 also rotates according to that rotation and the rollers 16 are pressed against a cam surface included in the input-side disc 2 by a cam surface formed on the cam plate 13, thereby pressing the input-side disc 2 toward the output-side disc 3.
A back surface side of the input gear 14 includes a cylindrical portion 14b. An input-side bearing 20 is fitted inside the cylindrical portion 14b. The input-side bearing 20 is limited of leftward movement along the shaft (supporting shaft) 1 direction by a flange portion 1a included in the shaft (supporting shaft) 1 at a left end portion thereof.
The left end portion of the shaft (supporting shaft) 1 is supported by the input-side bearing 20. The input gear 14 is rotatable relative to the shaft (supporting shaft) 1 via the input-side bearing 20. The input-side bearing 20 is an angular bearing.
When the pressing mechanism 5 presses the input-side disc 2 toward the output-side disc 3, reaction thereof is applied to the input-side bearing 20 as a thrust load via the cam plate 13 and input gear 14.
Also, the shaft (supporting shaft) 1 supports the output-side disc 3 in a freely rotatable manner with a bearing. The output-side disc 3 is arranged opposite to the input-side disc 2 with power rollers 4 clamped therebetween.
A back surface side of the output-side disc 3 is provided with an output gear 18 in a manner freely rotatable around the shaft (supporting shaft) 1. The output gear 18 is provided in a manner rotatable integrally with the output-side disc 3.
A back surface side of the output gear 18 includes a cylindrical portion 18b. An output-side bearing 21 is fitted inside the cylindrical portion 18b. The output-side bearing 21 is an angular bearing.
A cylindrical supporting member 22 is fixed to a right end portion of the shaft (supporting shaft) 1. The supporting member 22 is inserted in and fixed to the output-side bearing 21. Therefore, the output gear 18 is rotatable relative to the shaft (supporting shaft) 1 via the output-side bearing 21.
Furthermore, a ring-shaped fixing member 23 abuts against a flange portion 22a of the supporting member 22 and the fixing member 23 is fixed to the shaft (supporting shaft) 1. Therefore, the output-side bearing 21 is limited of rightward movement along the shaft (supporting shaft) 1 direction.
When the pressing mechanism 5 presses the output-side disc 3 rightward via the input-side disc 2 and the power rollers 4, a thrust load is applied to the output-side bearing 21 via the output gear 18.
In such a single-cavity toroidal continuously variable transmission, the input-side bearing 20 to support the thrust load applied from the input-side disc 2 and the output-side bearing 21 to support the thrust load applied from the output-side disc 3 are in the same size.